The present disclosure relates to methods for processing a sputtering target to obtain a sputtering target that has reduced particulation during sputtering and needs less burn-in time for optimum operation. The sputtering targets themselves, as well as methods for producing such targets, are also disclosed.
Sputtering is used to deposit a source material in the form of a thin film onto a substrate (e.g., in micro-electronics applications). The source material to be deposited is formed into a sputtering target with either rectangular or round shape or other geometrical shapes. The sputtering target is then bombarded with a beam of energetic particles (e.g., an ion beam or a plasma beam) in a controlled environment. Atoms of the source material are ejected from the sputtering target and deposited onto the substrate to form a thin film (e.g., a semiconductor wafer).
The procedure for forming a sputtering target with the desired dimensions and geometrical shape usually involves various mechanical machining steps (e.g. grinding, turning) that are very likely to introduce surface defects onto the sputtering target (e.g., cracks, contaminations and machining scratches, etc.). For example, operations such as lathing, milling, and grinding use extensive forces on the exterior surfaces of the sputtering target to cut/remove materials and form the desired shape and dimensions with high precision. Also, in order to avoid temperature increases of the work piece, various lubricants or coolants have to be used during machining. Surface defects such as grinding lines, scratches, embedded impurities, and contaminations are usually unavoidably present on the final finished surface of the sputtering target after machining. These surface defects cause undesirably high levels of initial particulation during sputtering. Particulation of a sputtering target refers to large particles being ejected from the surface of the sputtering target, rather than individual atoms/ions, and landing on the wafer. These particles can be considered to be contaminants because they affect and reduce device yield due to the resulting particle defects formed on the substrate. Particulation can also result in formation of nodules on the substrate, which has pronounced effects on the properties of the thin film.
The condition of the surface of the sputtering target, surface residual stress, and local density variations affect the occurrence of particulation. A smooth, defect-free, residual stress-free and contamination-free (i.e. clean) surface is desired for reducing initial particulation of a sputtering target.
A burn-in or preconditioning step may be used to remove any surface defects prior to using the sputtering target for material deposition on a substrate. During the burn-in step, the sputtering chamber cannot be used for production. This makes the burn-in process expensive in terms of both time and money. Reducing the preconditioning or burn-in time would result in savings and a reduction in ownership costs. Because it is common in the semiconductor industry to use a cluster of sputtering tools for continuous production, reducing particulation and minimizing burn-in time are both vital for highly efficient production.